The glass transition, segmental relaxations and viscoelastic behaviour of particulate-reinforced natural rubber

Abstract The role of filler particles in defining local changes to the dynamics of elastomer polymers – specifically in relation to the reinforcement of commercial elastomer systems – is as yet incompletely resolved. This work examines the glass transition of filled, crosslinked natural rubber in relation to filler reinforcement mechanisms using a variety of complimentary experimental techniques. Carbon black and precipitated silica filler particles with a wide range of surface areas, structures and surface activities are used as the reinforcing phase. No effect of the filler particles on the calorimetric glass transition is observed in terms of shifting, broadening or transition strength. Dielectric spectroscopy measurements show that the polymer relaxation times of the filled rubbers in the glass-to-rubber transition zone remain essentially equivalent to that of the corresponding unfilled material. Dynamic mechanical analysis demonstrates that the storage moduli of the filled elastomers are significantly amplified on the rubbery side of the glass transition. Elastic stiffening mechanisms are discussed in the context of contributions from filler networking. The reason for a distinct lack of evidence for filler-induced polymer modification may be due to the nature of polymer confinement associated with the imperfect dispersion state of the fillers in the sample and the fact that the fillers themselves are formed from aggregated primary particles rather than being true nanoparticulates.